This invention relates to brakes, and in particular to an improved brake plate, as well as a method and apparatus for manufacturing the plate.
The number of motor vehicles has increased greatly in recent years. There is an interest in methods of reducing the cost of manufacturing brakes and replacement parts on the part of both motor vehicle manufacturers and suppliers of parts for brakes. This increased use has also led to a significant increase in the after-market for brake replacement and repair. Brakes are also in increasing demand for motor vehicles such as airplanes, trains, bicycles, all terrain vehicles and motorcycles.
Brakes, as currently manufactured, combine two main parts, namely a plate (often called a backing plate) and a friction pad. The plate is mounted in a brake assembly, and may be formed by making a plate with a variety of bosses, holes, or other features for receiving and retaining the friction pad. The need to use high speed low cost manufacturing methods often results in irregularities in the plate which may lead to difficulties in attaching and/or retaining the friction pad on the plate during braking, when the friction pad is in contact with the rapidly turning brake rotor, or even during the pre-installation handling of the brake pad assembly.
There are a variety of known ways of attaching a friction pad to a plate. One such way is to attach the friction pad to the backing plates using rivets. One disadvantage of the riveting process is that it creates a rigid bond between the plate and the friction pad, which can, as a result of a sudden impact, lead to breaking of the friction pad. Furthermore, this process often requires one or more additional manufacturing steps with a consequent increase in cost. In addition, when the friction pad is worn down over time, the rivets become exposed and rub against the brake rotor, causing scoring on the rotor which is costly to repair.
Another, more recently developed method of mounting the friction pad on the plate is to use a pressurised molding process to mold the friction pad directly onto the plate. In this process, the friction pad may be prepared by blending the components of the friction pad into a pre-form or cake. A conventional pressurized molding system is used to mold the friction pad pre-form onto the plate. A layer of cement or glue if often applied to the contact surface of the plate to improve the adhesion between the plate and the friction pad.
As pressure is applied to the mold assembly, the pre-form becomes heated and begins to flow, filling the mold and covering the appropriate surface of the plate. In this process, the pre-form material is intended to flow into and around the various features to improve the bond between the plate and the friction pad.
The plate is subjected to a number of forces, such as the jarring of the moving vehicle, as well as vibration caused by the rotor and noise. The problem with the prior art processes and plates is that features, such as holes and bosses, stamped into the plate often provided insufficient shear and/or tensile strength in the bond between the friction pad and plate. When additional features are stamped into the plate to increase bond strength, additional manufacturing steps are required, adding to the cost.
The most common prior art features stamped into plates are circular holes. These holes often provide unsatisfactory results because, during the molding process, the pre-form cake does not completely fill all of the holes, which in turn, leads to deficient bonding between the plate and the pre-form. The incomplete hole fills can are clearly visible, and often raise quality concerns when inspected by buyers. The incomplete hole fills also have an aesthetically displeasing appearance, which can also make them less attractive to customers. Accordingly, it has become common practice in prior art plates to fill the incomplete hole fills with putty and to paint over them, to both hide the unsatisfactory molding results and to improve appearance. These additional manufacturing steps have the added disadvantage of increasing the cost of manufacturing the disc brake.
Furthermore, the holes stamped by prior art processes reduce structural strength of the plate, and make it more vulnerable to the various forces acting on it. These forces may distort the shape of the plate, leading to uneven wear on the friction pad, or can lead to structural failure of the plate.
Another problem with brake plates is caused by the heat generated by friction. The expansion and contraction values of the plate are different from those of the friction material. Braking generates heat so the plate and material are exposed to frequent heating and cooling. Since the expansion and contraction values differ, there may be a separation between the plate and the material, particularly where the plate is flat or has large flat areas. Rust can then form between the plate, which leads to noise and brake failure.
Accordingly, there is a need for a brake plate and a method of manufacturing same which can provide improved bonding with the friction pad without increasing the cost of producing the plate
It is an object of the invention to provide a plate which provides an improved bond between it and the friction pad, as well as increasing the structural strength of the plate, without increasing the cost of producing the plate. In addition, it is an object of the invention to provide a method and apparatus for manufacturing the plate which reduces time and cost by requiring fewer manufacturing steps, while at the same time retaining the structural strength of the backing plate.
Further features of the invention will be described or will become apparent in the course of the following detailed description.
The invention includes a plate for holding a friction material in a brake assembly, the plate comprising:
contact surface for attaching the friction material to the plate,
a second surface opposing the contact surface;
a plurality of retaining structures formed on the contact surface, each retaining structure comprising a projecting member extending from a point between the contact surface and the second surface, so that the member extends outwardly from the contact surface for engagement with the friction material. The retaining structure may further comprise a depression surface abutting the projecting member, the depression surface extending into the contact surface. The contact surface may be curved or substantially flat. The brake may comprise a disk brake or a drum brake. The plate may comprise integral retaining structures.
The retaining structures can be formed from the plate, and preferably cut or scored. In a variation, the projecting member may be a burr. The burr optionally comprises a hook shape, wherein a distal end of the hook points away from the depression adjacent to the hook. The retaining structures are optionally disposed in a plurality of rows. The rows are optionally substantially parallel. The rows may be usefully disposed longitudinally.
Preferably, the contact surface and the second surface of the plate define a perpendicular axis. The projecting member extends outwardly from the contact surface so that the projecting member is offset from the axis. The projecting member comprises a first end and a second end. The first end is connected to the plate. In a preferred embodiment, the second end is rotated with respect to the first end. The second end may also be offset from the first end so that the projecting member is bent in a hook shape.
Where the projecting member comprises a burr, the burr is preferably xe2x80x9ctwistedxe2x80x9d in that the second end is rotated with respect to the first end. Any degree of rotation is suitable within the tolerance of the cutting or scoring process.
The burr is also preferably xe2x80x9cbentxe2x80x9d in that the second end is offset from the first end. Any direction is suitable within the tolerance of the cutting or scoring process.
In a further embodiment of the plate, the twisted and bent burrs are disposed in rows. The rows may comprise burrs twisted and bent alternately in counterclockwise and clockwise directions. Alternatively, the rows may comprise burrs twisted and bent in alternating rows of counterclockwise- and clockwise-directed burrs.
The invention also includes a method of manufacturing a brake plate for securing a friction material to a contact surface thereof, the method comprising providing:
a contact surface for attaching the friction pad to the plate,
a second surface opposing the contact surface;
a plurality of retaining structures formed on the contact surface, each retaining structure comprising a projecting member extending from a point between the contact surface and the second surface, so that the member extends outwardly from the contact surface for engagement with the friction pad.
The invention includes a brake plate, preferably a drum brake plate or a disc brake plate made according to a method of the invention or with the apparatus of the invention.
In one method, the retaining structures are formed by cutting the contact surface. The retaining structures are alternatively formed by scoring the contact surface. In another variation, the retaining structures are formed by cutting a plurality of rows of retaining structures on the contact surface. The rows are optionally substantially parallel and/or disposed longitudinally.
In one embodiment, the cutting is done by a plurality of knives, each knife having a cutting edge, the edge having a plurality of teeth connected thereto. Each retaining structure is preferably made by one tooth. Each tooth preferably cuts a projecting member from the contact surface to form an adjacent depression. The knives are preferably disposed longitudinally in relation to the plate. The knives may be substantially parallel. Adjacent knives preferably move in opposing directions. The plurality of knives are preferably moving parallel to the contact surface prior to impacting the plate. The plurality of knives preferably commence to move parallel to the contact surface upon impact with the plate. The plate may be stationary while it is punched by the knives. The knives are optionally fixed in the direction perpendicular to the contact surface and the plate is impacted onto the knives.
Another variation of the invention relates to an apparatus for manufacturing a brake plate having a plurality of retaining structures formed on a contact surface thereof for retaining a friction material, comprising:
a means for cutting a plurality of retaining structures on the contact surface, each retaining structure comprising a projecting member extending from a point between the contact surface and the second surface, so that the member extends outwardly from the contact surface for engagement with the friction pad, the cutting means being adapted to move generally parallel to the contact surface to cut the retaining structures;
a driving means for impacting the cutting means and the contact surface of the plate to form the retaining structures.
The cutting means preferably comprises a plurality of knives, each knife having a cutting edge, the edge having a plurality of teeth connected thereto, each tooth adapted to form one of the plurality of retaining structures upon impact with the contact surface.
The apparatus optionally further comprises:
at least one drive member slidably connected to at least one side of each of the plurality of knives;
at least one slide member slidably connected to the drive member;
During impact between the knives and the contact surface, the slide member is preferably adapted to move away from the contact surface, the slide member being adapted to move the drive member generally parallel to the contact surface, the drive member being adapted to move the knives generally parallel to the contact surface.
The slide member may have an inclined sliding surface, the sliding surface being adapted to move the drive member generally parallel to the contact surface upon movement of the slide member. The at least one slide member can be two slide members, the at least one drive member can comprise first and second drive members, and the at least one side of the each of the knives can comprise a first side and a second side, wherein first drive member is proximate to the first side of at least one knife, and the second drive member is proximate the second side of the remaining knives. The first and second sides of alternate knives are preferably proximate to the first and second drive members, respectively. The adjacent knives preferably move in opposing directions upon impact with the contact surface. The apparatus may further comprise a return means for returning the knives to a starting position. The return means is optionally at least one spring attached to a first and second slide rod, the slide rods being located within a first and second guide slots defined proximate to the first and second side of each knife. The plurality of knives are preferably disposed longitudinally in relation to the plate. The apparatus knives are preferably substantially parallel to each other.
The slide member and the plurality of knives are preferably adapted to move generally parallel to the contact surface prior to impact with the plate. The plurality of knives are preferably adapted to move parallel to the contact surface upon impact with the plate. The plate is optionally stationary while punched by the knives. The knives are optionally fixed in the direction perpendicular to the contact surface, and the plate is driven onto the knives. The impacting means optionally comprises a press having a top movable portion and a bottom stationary portion.
The apparatus of optionally further comprises:
a base plate secured to the top portion of the press;
two side plates secured to the base plate, the side plates projecting downwardly therefrom;
a positioning means for maintaining the knives in proximate to each other; the positioning means being connected to the side plates;
a force adjustment means for adjusting the force of impact of the knives against the contact surface, the force adjustment means having a pressure plate generally parallel to the base plate and at least one spring disposed between the base plate and the pressure plate, the pressure plate being connected to the knives;
wherein the first and second slide rods are suspended from the base plate.
The first and second sliding members preferably impact the bottom portion of the press prior to the knives impacting the contact surface, thereby causing the knives to move generally parallel to the contact surface prior to impact of the knives against the contact surface. The first and second sliding members preferably impact the bottom portion of the press substantially simultaneously with the knives impacting the contact surface, thereby causing the knives to move generally parallel to the contact surface substantially simultaneously with impact of the knives against the contact surface.